Transpose key calculator: move chords, scales and guitar capo positions between any key by semitone, with note mapping and capo fret shown. Free, private.
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Calculation details
Every figure above is calculated locally in your browser from the assumptions shown. No inputs are sent anywhere. See the methodology section below for how this tool works.
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Worked example: C to Eb
The calculator stores the 12 key labels in a fixed chromatic order: C, C#, D, Eb, E, F, F#, G, Ab, A, Bb, B. Each label sits at a chromatic index: C is 0, D is 2, Eb is 3. To transpose from C to Eb, it finds index 0 for C and index 3 for Eb, then computes (3 - 0 + 12) mod 12 = 3. That gives 'up 3 semitones' and 'Equivalent to: 3 half-steps'. Musically that is the C minor third: every C, D, and E in your chart becomes Eb, F, and G.
The +12 in the formula handles the wrap-around case. Take F to C: F is index 5, C is index 0, so (0 - 5 + 12) mod 12 = 7, reported as up 7 semitones. Without the +12 the raw difference would be -5, and the modulo would still land on 7 in JavaScript for this case, but the explicit +12 keeps the result a positive step count in every input, including F# to F, which is (5 - 6 + 12) mod 12 = 11.
Limits worth knowing before you transpose
The label list uses fixed spellings, so enharmonic keys are not interchangeable the way theory would allow. There is no Db, D#, Gb, or A#; if your piece is in Db you pick Eb's slot (index 1 as C# or index 3 as Eb) and the step count still comes out right, but the printed key name will not match your sheet music's spelling. Similarly C# and Db both map to index 1.
The tool also reports only the shortest clockwise distance. B down to C is physically 1 semitone downward, but the calculator returns up 11 semitones, because it always measures forward in the chromatic cycle and only says 'no change (same key)' when the two keys match exactly. And it moves the key center only: transposing C to G shifts every note up 7 half-steps but keeps the mode, so a C major chart becomes G major, while a C minor chart becomes G minor. It will not convert major to minor or re-fingering for a capo.
